Device for preventing excessive wear on car-lighting dynamos



H. D. ROHMAN.

DEVICE FOR PREVENTING EXCESSIVE WEAR 0N CAR LIGHTING DYNAMOS.

' APPLICATION FILED AUG-I9, I9I6.

1,338,041, Patented Apia-27, 1920.

/0 43 l J. 9 E ,4 I E12 emf-J g FIG. 2.

A'TTOEM EIK FI.

UNITED STATES. anna OFFICE.

HARRY D. ROHMAN, OF NEW YORK, N. Y., ASSIGNOR, BY MESNE ASSIGNMENTS TO J. STONE & COMPANY, LIMITED, OFDEPTFORD, ENGLAND.

DEVICE FOR PREVENTING EXCESSIVE WEAR ON GAK-LIGETING DYNAMICS.

Specification of Letters Patent. Patented .Apr, 27, 1920 Application filed August 19, 1916. Serial No. 115,777.

To all whom it may concern:

Be it known that I, HARRY D. ROHMAN, a citizen of the Republic of Switzerland, residing at New York city in the county of New York and State of New York, have invented certain new and useful Improvements in Devices for Preventing Excessive Wear on Car-Lighting Dynamos, of which the following is a specification.

This invention relates to a device for preventing excessive wear of the dynamos employed in electrical car lighting systems and the like and it is particularly useful in connection with car lighting systems in which a dynamo of the speed controlled type, such as the slipping belt type, is employed, the device in such instance preventing excessive slipping of the belt and wearing of the belt and pulleys.

It is one of the primary objects of my invention to provide an improved device of the character specified which is simple and economical in construction and which may be readily installed in standard forms of equip ment.

Another of the primary objects of my invention resides in the provision of an improved device for confining the amount of belt slippage within predetermined limits.

The foregoing, together with such other objects as may'hereinafter'appear or are incident to my invention I attain by means of a construction, one embodiment of which I have illustrated in the accompanying drawin s wherein igure 1 shows my improved device in cross-section as applied to a single battery car lighting system embodying a slipping belt type of dynamo, the system being shown in diagrammatic form; and Fig. 2 is an enlarged section of a detail of my invention.

Referring now to the car lighting "equipment as diagrammatically illustrated by the drawings, it will be seen that I have therein, indicated a dynamo 7 which is driven from a pulley on the car axle by means of a slipping belt 8 which passes over the dynamo pulley 9. 10 and 11, respectively indicate the positive and negative leads by means of which the battery 12 and the usual translating devices, such as lamps, fans and the like are supplied.

The numeral 13 indicates a standard form cf automatic cut-in and cut-out switch which is adapted to be closed when the dynamo voltage shall have reached a point at which 1t is equal to or greater than that of the battery. The dynamo preferably is so constructed that this voltage will be obtained at very low train speeds, say for example, 10 miles per hour, at which time it will be safe to close the circuit. The dynamo is of a shunt wound type and I have diagrammatically indicated the field thereof as at 14. The operation of this general form of equipment is substantially as follows: On starting up of the train the dynamo rapidly builds up and furnishes full output at the very low train speed of 10 miles per hour, after which the belt begins to slip and the armature thereafter rotates at approximately constant speed. When the train speed shall have increased to about 30 miles per hour, the belt will slip at about the ratio of 1 to 3, this ratio being found not excessive. If however, the speed of the train increases above 30 miles per hour which is of course frequent, the amount of belt slippage would be greatly increased, which would result in excessive wear and tear on the belt and pulleys, which of course would have a tendency to greatly decrease the life thereof. It is one of the objects of my invention to overcome this difiiculty and I have accomplished this by the following equipment.

I employ an automatic control device A which preferably comprises a centrifugal make and break mechanism driven in anyone of a number of different ways. In the preferred form, this control device comprises a casing 15, anti-frictionally supported on a shaft 16 which is suitably mounted adjacent to the axle pulley so that the casing will be in frictional engagement with the periphery of the pulley.

In the casing of the control device and mounted on theshaft 16, I provide a pair of fixed contact plates 18'and 19 which are insulated from each other and from the shaft 16. The plates are spaced apart and are beveled on their inner edges. Wires 2-0 and 21 lead from the plates 18 and 19, respectively, to opposite sides of a resistance 22 located in the circuit of the field. A pair of oppositely arranged conical brush contacts 23 are slidably mounted on stems 24:

I adjustably carried in the casing 15, and are normally held engaged with the plates 18 and 19 by springs 25 which also are adjustable. In normal closed position, the brushes 23 short circuit the resistance 22.

The operation is as follows: As hereinbefore pointed out when the train has started, the generator builds up and furnlshes full output at about 10 miles per hour, whereupon the automatic switch 13 is closed, and the armature rotates at a substantially uniformrate of speed owing to the slipplng of the belt. The belt continues to slip until the train reaches a speed of about approximately 30 miles per hour at which time as above indicated the ratio of belt slippage is about 1 to 3. The automatic control device and the springs 25 however, are so arranged that when the train reaches a speed of about 30 miles per hour, the contact brushes 23 are moved out of engagement with the plates 18 and 19 by the action of centrifugal force as a result of which the wires 20 and 21 are disconnected and the resistance 22 is placed in the field 14. The effect of inserting the resistance into the field is that the field will be weakened and the armature of the generator will immediately follow the speed of the train, that is to say, the armature speed will increase in direct ratio with the train speed. The resistance 22 may have any predetermined value, but I prefer to so calibrate it that the strength of the field may be reduced to an. amount that the dynamo will deliver at this train speed of 30 miles per hour practically the same output as was obtained from the rate of 10 miles per hour to 30 miles per hour, but without slippage of the belt. Thus, from about 10 miles per hour to 30 miles per hour the constant output predetermined by the engineer is obtained because of the slippage of the belt, while at the rate of 30 miles per hour substantially the same predetermined constant output iscobtained without slippage. As the train speed increases above 30 miles per hour it will be readily seen that before the ratio of belt slippage of 1 to 3 is again obtained, the train speed will have to increase above 90 miles per hour. It will be at once seen that the. practical limits of present day train speed are more than covered and that at all times, the rate of the slippage of the belt is not more than 1 to 3. As above indicated this rate is quite practical for train lighting systems and when the slippage is confined within these limits, the wear and tear on the parts is not excessive;

On slowing down of the train to 25 miles per hour the centrifugal force of the control device will have been reduced to such an extent that the electrical contacts are again made between contact plates 18 and 19, thereby short circuiting the field resistance 22. The output of the generator, however,

will be held up to its predetermined constant value because the belt will slip, until such a time as the train speed is reduced below 10 miles per hour at which time the generator will be disconnected entirely by the opening of the automatic switch 13.

Apart from the advantages obtained by preventing excessive wear and tear, my improvement considerably increases the efficiency of the entire equipment and it will be readily seen that as soon as the train reaches a speed of 30 miles per hour, the field strength is automatically weakened regardless of any electrical condition. But even with this weakened field, owing to the fact that the belt will, thereafter, not slip or slip but little until a relatively high train speed is attained, the output is somewhat increased, even though the belt tension remains the same, which is a particularly valuable feature in heavy winter weather.

From the foregoing it will be seen that my invention is particularly useful in local service or other service, the conditions of which are such that full output must be had at very low train speeds, while at the same time the speed of the train may at times be very high, which of course would result in excessive wear in the absence of equipment of the character described. The invention is also useful in other kinds of service where there are wide ratios between the speed at which the dynamo delivers full output and maximum train speeds, such for example as where a car is used on short local runs on one day and long through runs on the next.

In other types of speed controlled systems, the device will operate in the same way to relieve the driving mechanism corresponding to the slipping belt of the system shown and described. One of the more specific of the advantages of my invention is that the brushes have a self-cleaning contact 011 plates 18 and 19.

I claim:

1. In a car lighting system, the combination of a dynamo-electric machine, a slipping belt therefor slipping at a predetermined standard or rate of train speed, and means under the control of the train speed for automatically determining a new standard or rate at which the belt slips.

2. In a car lighting system, the combina tion of a dynamo-electric machine, a slipping belt therefor, and automatic means for maintaining the belt slippage within predetermined limits regardless of train speeds, said means being under the control of train speed.

3. In a car lighting system, the combination of a dynamo-electric machine, a slipping belt therefor, and means for maintaining the belt slippage within predetermined lnnits regardless of train speeds, said means including a resistance and means under the control of train speed for inserting said resistance into the field.

4. ,In a car lighting system, the combination of a dynamo-electric machine, a slipping belt therefor, sl ipping at a predetermined standard or rate of train speed, and means for altering the standard or rate at 1 which the belt sli s, said means including a tained without belt slippage when the train reaches a predetermined speed.

6. In'a car lighting system, the combination of a dynamo, compensating means adapted to maintain a substantially constant armature speed between certain rates of train speed thereby maintaining substantially constant output, and means whereby the same standard of output is maintained without compensation when the train reaches a predetermined speed.

7. In a'car lighting system, the combination of a dynamo, slipping compensating means for maintaining a substantially constant standard of output between certain rates of train speed, and means for maintaining the substantially same standard of output without slippage when the train reaches a predetermined rate of speed.

8. In a car lighting system, the combination of adynamo, compensating means for controlling armature speed operable at a predetermined standard, and automatic means under the influence of train speeds for altering the standard at which said first means operates.

9. In a car lighting system, the combination of a dynamo, a car axle driven slipping belt drive therefor, a resistance element normally in circuit with the field of the dynamo, a circuit for short circuiting said resistance, and a centrifugal governor operated from a rotating part of the car, normally completing said circuit, and adapted to break said circuit when the train reaches a predetermined speed.

In testimony whereof I have hereunto signed my name.-

HARRY D. ROHMAN. 

